1. Technical Field
The invention is generally related to the field of micofluidics. More specifically, the invention relates to novel microfluidics chips and methods of using same which address the problem of contamination of patterned surfaces in such devices.
2. Background Art
Currently known microfluidics chips typically comprise two mating halves or wafers, each having patterned surfaces. The patterns are such that when the two wafers are placed adjacent each other, a microfluidics cavity or flow channel is formed between the wafers. The two wafers are bound together in a process referred to as wafer bonding. One or more fluids is forced through the microfluidics channel, for example a sample and a reagent. One problem with this arrangement is that in order to reuse this wafer bonded microfluidics chip device to analyze a new sample, the microfluidics channels must be thoroughly cleaned, which is difficult and time consuming. These problems can be understood by considering the example of handling a blood sample. In most respects it is undesirable that the blood, or any related biological product, contact the patterned surfaces of the wafers. If contamination occurs, the microfluidics chip patterned surfaces must be cleaned before the device can be used for a new sample.
U.S. Pat. No. 6,082,185 describes a compact fluid circuit card having a main body with internal sensing elements and with fluidic circuit components located on both its front and back surfaces. The cards are described as being made inexpensive enough to be disposable by forming its main body and all of its fluidic circuit components so that they are suitable for being integrally formed in one piece by injection molding from plastic, and by using thin strips of adhesively attached material for the main cover bodies, and valve membrane strip. The patent describes the use of heat shrinkable plastic as one suitable valve membrane material. While the patent does describe prevention of cross contamination between liquids in the card by using plastic valve membranes, there is no provision for preventing contamination of the actual fluidic circuit components.
Patent Cooperation Treaty International Publication No. WO 02/18827 A1, published Mar. 7, 2002, describes microfluidics valves which include a microconduit for carrying fluid therethrough and at least one microactuating mechanism for selectively deflecting at least a portion of a wall of the microconduit, thus occluding fluid flow through the microconduit. This publication describes a microfluidics valve that is opened or closed by heating and expanding a flexible material to open and close the microfluidics channels. The flexible material may be selected from materials including, but not limited to, “silicon rubber, natural rubber, polyurethane, PVC, polymers and any other similar flexible mechanism known to those of skill in the art.” This document does not disclose or suggest protecting flow channels in microfluidics chips from contamination.
U.S. Pat. No. 6,443,179 describes a method for electro-microfluidics systems packaging. The patent describes “a new architecture” relying on two scales of packaging to bring fluid to the device scale (picoliters) from the macro-scale (microliters). The larger package consists of a circuit board with embedded fluidic channels and standard fluidic connectors (referred to as a fluidic printed wiring board). The embedded channels connect to the smaller package, referred to as an electromicrofluidics dual-inline-package (EMDIP) that takes fluid to the microfluidics integrated circuit (MIC). The fluid connection is made to the back of the MIC through etched holes that take fluid to surface micromachined channels on the front of the MIC. While adhesive layers are used to bond different components together, the fluidic passageways are nonetheless exposed to the sample. Essentially the adhesive films function as gasket materials.
U.S. Pat. No. 6,068,751 describes a microfluidics delivery system that allows control of flow of a fluid through elongated capillaries that are enclosed along at least one surface by a layer of a malleable material. An electrically powered actuator included in the systems extends toward or retracts a blade from the layer of malleable material to either occlude or open capillaries. Reservoirs included in the pouch together with the capillaries supply fluids whose flow is controlled by movement of the blades. This patent does describe a microfluidics system in which an actuator portion of a valve does not become contaminated during system operation and in fact the actuator portion of the valves are reusable without cleaning. However, the microfluidics delivery systems of this particular patent require electromechanical valves to stop and start flows of fluids, with components that are irregularly shaped, and do not employ a vacuum for shaping of barrier films.
There is a need in the microfluidics art for microfluidics chips and methods of using same, which feature little or no raw sample contamination of microfluidics flow channels.